Made it possible to use assoc_mem in vector mode

Can now pass in a return_vec boolean parameter when creating
instances of the AssociativeMemory class. When this is true, calls
to unbind_and_associate will return the correct vectors rather than
the key of the correct vectors.
GPUCleanup now has param for blocking gpu output

Can now give a parameter to GPUCleanup which suppresses output from
the GPU. Will be used mainly in tests, since output from the GPU is
not captured by nosetests.
Added tests

Added tests, and added attribute to the tests for the purpose of test
selection via the nost plugin Attrib. Most neural tests have
speed=slow, and the rest have speed=fast. To run all fast tests, we
can use "nosetests -a speed=fast".